Here are a few tips for adding water plants to your garden feature.

1. Pay attention to how aggressive the water plants are. Some, such as cattails, can spread amazingly fast. While that might sound like a good thing, plants that can grow 5 – 6 feet tall in a single season and reproduce at an alarming rate could quickly overrun a pond. Either avoid using such plants, or confine their roots to a pot to prevent an imminent takeover.

2. On the flip side, growing water plants is a relatively painless job. After all, they don’t require watering! What they do require is planting at the proper depth (often specified on water plant tags; if not, inquire at your local garden center), exposure to the right amount of light (especially for flowering plants), and occasional feeding via water-plant spikes stuck into the planting medium twice a year.

3. Choose the right plants for you. Here’s a look at the four broad types of water-garden plants, all of which you would likely find in a healthy, natural environment.

FLOATERS: As the name implies, these plants float on top of the water. Their leaves and flowers remain above water, while their roots dangle below. Floaters, which include water lettuce, water hyacinth, and duckweed, provide shade and food for fish and other wildlife. Some species also act as natural water filters.

Most pond owners love floaters because they shade the water, which in turn cuts down on the growth of algae. However, if they spread to the point where they cover more than two-thirds of the pond’s surface, they could wind up trapping carbon dioxide and other dangerous gases below. The solution is easy enough. Simply scoop out any excess plants and throw them on the compost pile.

WATER LILIES AND OTHER DEEP-WATER PLANTS: Rooted in pots at the bottom of the pond, water lilies and their look-alike cousins, lotuses, send up leaves that float on the surface. Similar to floaters, these leaves shade the water, lowering temperatures and helping to control algae.

Water lilies come in two basic types: tropical and hardy. Tropical water lilies grow from tubers and are prolific bloomers. Their blossoms are suspended on stems rising above the water surface.

Hardy water lilies grow from rhizomes and are somewhat less showy. Their blossoms are smaller and, for the most part, float on the water’s surface.
Although tropical water lilies are showier, they can’t sustain temperatures much below 60 degrees F., so unless you’re willing to provide protection for them when the temperatures begin to drop, stick to hardy lilies.

SUBMERGED PLANTS: Submerged plants, such as water milfoil and hornwort, can also be grown in pots at the bottom of the pond, although their foliage remains completely underwater. While they do add small amounts of oxygen to the water, their main allure is in providing cover for fish-—particularly young fry—-and in absorbing carbon dioxide and minerals, resulting in slower algae growth. They also help filter the water.

Submerged plants are usually sold in bunches of six stems. Plant one bunch about every 3 square feet. Submerged plants do not need soil, which can foul your pond’s water; instead, use sand or gravel. Also, you won’t need to fertilize submerged plants, since their leaves draw their nutrients directly from the minerals dissolved in the pond. Since some varieties do better than others, mix several different ones to see which grow best for you.

MARGINALS: Marginal water plants take their name from that marginal area between shore and pond. While their roots are submerged, their leaves grow out of the water. Most marginals are shallow water plants that may be grown in pots or directly in the gravel on shallow shelves at the edge of the pond. Many marginals, such as iris and arrowhead, double as bog plants. In the water, they're best grown in containers that you can lift for grooming and dividing (splitting into smaller plants when they are overgrown), which will prevent them from spreading too quickly and becoming invasive.

Marginal plants are prized mostly as ornamentals. They add color and form to the aquascape and help the water garden blend visually into the rest of the landscape. They also help to filter out some of the impurities in the water. You may want to try putting several plants of one marginal variety in one large container. Don’t put several different plants in a single container, as the stronger ones will outgrow and eventually kill off the weaker ones.